1. Field of the Invention
The present invention relates to a dry toner for developing static charge images formed by electrophotography, electrostatic printing method, electrostatic recording method, and the like.
2. Description of Related Arts
Various techniques have heretofore been used in order to improve fixing strength at low temperatures for fixing toners for developing static charge images for copiers and printers. Investigation has been made mainly on binder resins in the toners for developing static charge images.
For example, there have been used a method in which the distribution of the molecular weight of the binder toner is broadened and a method in which high molecular weight parts of the binder resin are crosslinked. However, these methods have problems that it is inevitable to decrease the glass transition temperature of the toner in order to maintain the fixing strength of the binder resin at a sufficient level, which deteriorates the storage stability of toners for developing static charge images containing it, and that it is difficult to give the toner a sufficient fixing strength even when it is tried to improve the fixing strength while maintaining its storage stability at the same level.
Another method has been proposed, in which a small amount of an auxiliary resin that is highly crystalline and has a low melt viscosity is added to the binder resin which is a main component of the toner for developing static charge images, thereby increasing improving the fixing strength of the toner. Although this method gives rise to good results with respect to the fixing strength of the toner and the storage stability of the toner due to the highly crystalline auxiliary resin added without decreasing the glass transition temperature, the melt viscosity of the toner at the time of hot roll fixing decreases abruptly and a phenomenon of off-set tends to occur due to weak aggregation of the toner while it is molten. In order to obviate the above-described problems, it has been proposed to add a highly crystalline polyolefin or natural wax which has a sharp melt viscosity characteristics to the toner. However, the polyolefin wax has a problem that carbon, charge control agent and the like which are to be dispersed in the toner for developing static charge images are difficult to be dispersed, resulting in that it is difficult to obtain a uniform toner for developing static charge images. On the other hand, natural wax has a problem that its static stability, environmental characteristics and particularly storage stability deteriorate remarkably.